David Cameron has denounced a "sexist" online campaign to sack BBC political editor Laura Kuenssberg.
Speaking during Prime Minister's Questions, Mr Cameron said people should be able to speak freely in a democracy, but he criticised the "appalling" behaviour of social media trolls.
"Some of the things people say on Twitter knowing that they are in some way anonymous are frankly appalling and people should be ashamed of the sort of sexist bullying that often takes place," he said.
More than 35,000 people signed a petition, which has since been deleted, calling for Ms Kuenssberg, a former ITV News business editor, to lose her job.
The petition claimed that Ms Kuenssberg is biased against Labour - most recently in her coverage of last week's local and regional elections.
Many of the comments used by people who shared the petition on Twitter featured offensive and sexist language.
Earlier this year, both Ms Kuenssberg and her BBC colleague Andrew Neil were targeted by a petition calling for them to be dismissed over the on-air resignation of Labour and Co-operative Party MP Stephen Doughty.